The field of the present invention is fluid dispensing devices that use an expandable elastomeric bladder for the dispensing force.
There are many applications in consumer products, industrial applications, and medical devices for propelling a fluid or other flowing, dispensable products out of a container. The most popular type of dispenser is the aerosol can, a pressure container having a propellant gas for expelling fluids. Disadvantages of an aerosol can include the volume of product wasted and left in the container after all the propellant is consumed, the potential for explosion of a pressurized vessel, and damaging effect to the environment caused by certain propellants such as chlorofluorocarbons (CFC).
There are many existing bladder type dispensing devices. In order for a bladder type dispensing apparatus to dispense the maximum amount of product, the bladder is prestressed in the empty condition with a mandrel. The elastomeric bladder may then dispense the maximum amount of fluid as it returns to its beginning unfilled state.
There have been several methods devised to provide the prestressing of the elastomeric bladder. Gortz et al., U.S. Pat. No. 3,698,595, stretches the resilient bladder over an external tapered mandrel. Another external prestressing method is disclosed in Gortz et al., U.S. Pat. No. 3,907,169, in which a bladder is wrapped around and anchored at one end to a curved external support rib.
The present invention is more closely related to an internal prestressing mandrel such as disclosed in Jacuzzi, U.S. Pat. No. 3,361,303 which has a solid internal prestressing stem with a wedge shaped channel along one side thereof. Roper et al., U.S. Pat. No. 3,738,538 also discloses an internal mandrel which prestresses the bladder in both the axial and radial directions.
However, none of the existing devices have devised or even recognized the requirements for a simple and inexpensive prestressed bladder system which is reliable, meets storage requirements, and provides constant flow characteristics obtained by the present invention.